Throughout the world there is increasing interest in converting renewable lignocellulose material to usable products such as ethanol. Conversion of wood to ethanol has been practiced during wartime due to a shortage of liquid fuels. Reported in Ind. & Eng. Chem. Vol. 38 No. 9, page 890 (1946). Because of high pressures, high temperatures, low yields and consumption of chemicals the conversion was found to be uneconomical for peacetime use. Present day interest in hydrolysis of Biomass, often termed lignocellulose material, is to provide an alternative fuel source to avoid dependence on unreliable imported petroleum crude oil for liquid fuels. Biomass often contains hemicellulose and lignins accompanying the cellulose contained in the lignocellulose material. Biomass is a term used to describe renewable material containing cellulose. For example, paper, pulp, wood waste, sawdust, municipal solid waste (MSW) and agricultural wastes, all are herein refereed to as lignocellulose material. The hemicellulose and amorphous cellulose of a lignocellulose material is easily hydrolyzed to form sugars for fermentation in a process called pre-hydrolysis which leaves a residue containing lignins and un-hydrolyzed crystalline cellulose. Pre-hydrolysis consists of the reaction of water with a lignocellulose material in the presence of a catalyst, usually sulfuric acid. The residue from pre-hydrolysis contains lignins, un-hydrolyzed hemicellulose and un-hydrolyzed cellulose and is consequently a lignocellulose material.
It is well known that a high concentration of sulfuric acid will hydrolyze cellulose and hemicellulose at low temperatures to produce sugars for fermentation.
A state of the art process being developed by workers at the University of Arkansas is reported in FY 1997 BIOCHEMICAL conversion/ALCOHOL FUELS PROGRAM, Annual Report page 85. It employs high concentration of sulfuric acid to convert corn stover to sugars. Described is a scheme to separate sugars contained in the concentrated sulfuric acid using a heavy boiling solvent to dissolve the sulfuric acid and a low boiling solvent to dissolve the heavy boiling solvent. They also reported that this method has a loss of solvents and a loss of sulfuric acid, which is neutralized with lime. Reported in the above named report, on page A-15, is a plan by TVA to develop a high concentration of sulfuric acid process. The current focus of TVA is to develop an inexpensive process for recovering the high concentration of sulfuric acid. Thus recovery of the sulfuric acid is reported as an unsolved problem. The problem with these methods is the failure to cost effectively recover concentrated sulfuric acid. Consequently it is believed that no satisfactory recovery method has yet been developed.
The present interest is related to concentrated sulfuric acid used to produce fermentable sugars contained in a lignocellulose material and the separation of sulfuric acid from sugars formed. Solids, substantially free from sulfuric acid, contain precipitated fermentable sugars. The fermentable sugars are then dissolved by a broth from fermentation. The dissolved fermentable sugars are then fermented in a fermentation vessel to form a fermentation broth. The concentrated sulfuric acid, separated from the fermentable sugars, is recycled to produce additional fermentable sugars.
Thus many of the limitations and disadvantages of the prior art to recover sulfuric acid employed to produce fermentable sugars will be obviated.
Therefore an object of this invention is to employ concentrated sulfuric acid to produce fermentable sugars from a lignocellulose material.
Another object of this invention is to economically separate sulfuric acid from lignins and sugars formed from a lignocellulose material and to supply concentrated sulfuric acid for recycle.
An additional object of this invention is to ferment sugars formed from a lignocellulose material contained in sterilized ethanol extracted solids.
A further object of this invention is to produce lignins substantially free of sugars and sulfuric acid formed from a lignocellulose material.
Still another object of this invention is to produce a yield of hydrolysis of cellulose and hemicellulose nearing 100%.
Yet another object of this invention is to operate the method in a closed environment.
Additionally another object of this invention is to operate and accomplish low energy consumption.
With the above and other objects in view, this invention relates to the novel features and alternatives and combinations presently described in the brief description of the invention.